Ansys Harmonic Acoustics for Speech and Noise Evaluation

Introduction to Ansys Harmonic Acoustics

Ansys Harmonic Acoustics is commonly used to investigate noise transmission and acoustic responses within engineered systems. This article demonstrates how the same transfer-path methodology can be extended to evaluate speech transmission, noise transmission, and communication performance. Using a simplified vehicle-cabin example, transfer functions for both speech and noise sources are generated and combined to evaluate the Signal-to-Noise Ratio (SNR), providing a foundation for future speech intelligibility studies using Ansys Sound.

Speech Transmission Path Configuration

As an illustration, the figure below shows a simplified vehicle-cabin Harmonic Acoustics model with a passenger-position talker source (TS) and virtual listener locations positioned at the Driver’s Left Ear (DLE) and Driver’s Right Ear (DRE).

To investigate communication performance, a passenger-position talker source was introduced into the cabin, and responses were extracted at virtual listener locations corresponding to the driver’s ears.

Unlike traditional cabin acoustics investigations that focus primarily on interior sound-pressure levels, the objective here is to characterize how speech energy propagates from one occupant to another. By treating speech as an acoustic source and the driver’s ears as listener locations, Ansys Harmonic Acoustics can be used to generate source-to-listener transfer functions that describe communication performance throughout the enclosure.

The source is represented as a monopole pressure excitation with a normalized amplitude of 1 Pa and a phase angle of 0°. While simplified, this approach provides a practical mechanism for evaluating speech propagation without requiring detailed vocal tract or loudspeaker modeling.

The resulting transfer functions contain both amplitude and phase information and therefore provide significantly more insight than simple sound-pressure-level predictions. These transfer paths form the basis for evaluating how effectively speech is conveyed from one occupant to another.

Noise Transmission Path Configuration

The same vehicle-cabin Harmonic Acoustics model can be used to evaluate an external monopole source representing a form of unwarranted exterior noise.

Communication performance depends not only on speech propagation but also on how competing noise enters the listener environment.

The external monopole source represents a simplified noise excitation and allows exterior-to-interior propagation to be investigated using the same transfer-path methodology employed for speech transmission.

Like the speech source, the external source was normalized to 1 Pa, allowing direct comparison of transfer-path behavior without introducing source-strength bias.

Ansys Harmonic Acoustics and the Importance of Phase Information

Many acoustic investigations focus exclusively on amplitude. However, Harmonic Acoustics generates complex pressure responses that include both amplitude and phase. The complex acoustic pressure can be expressed as:

Phase information provides insight regarding:

• Reflection paths
• Travel-time effects
• Diffraction behavior
• Constructive interference
• Destructive interference
• Resonance activity

At 1000 Hz, large phase differences were observed between the speech and noise transfer paths for the vehicle model shown above.

These phase differences confirm that acoustic energy reaches the listener through significantly different propagation paths, despite both listeners occupying the same passenger compartment.

This is one of the key advantages of Ansys Harmonic Acoustics. It provides information extending well beyond conventional sound-pressure-level measurements and enables engineers to investigate how geometry, source location, and reflections influence communication performance.

Communication Performance and Signal-to-Noise Ratio

Communication effectiveness depends not on speech or noise independently, but on the relationship between them.

Signal-to-Noise Ratio (SNR) is defined as:

For the above case study,

Signal-to-noise ratio provides one of the most direct indicators of communication performance.

The most significant observation occurs at 1000 Hz.

Although the two listener locations are separated by only a relatively small distance, the DRE experiences approximately 18.3 dB of communication margin, while the DLE experiences approximately 9.7 dB.

This result demonstrates how communication quality can vary substantially within the same enclosure.

It also illustrates why evaluating speech or noise independently may not provide sufficient insight. Only by combining both transfer paths does the communication-performance picture emerge.

Key Observation: Two listener locations separated by only a small distance can experience dramatically different communication environments.

This is one of the most important findings of the study and highlights the value of location-specific transfer-path analysis.

Why Listener Position Matters

The acoustic wavelength is given by:

where:

• c = speed of sound
• f = frequency

As wavelength decreases,

• Reflection effects become increasingly important.
• Interference patterns become stronger.
• Acoustic gradients become steeper.
• Spatial variability increases.

This explains why relatively small changes in listener position can produce significantly different acoustic responses.

Ansys Harmonic Acoustics Conclusions

This study demonstrates that Ansys Harmonic Acoustics can provide substantially more value than traditional sound-pressure-level prediction alone. While Harmonic Acoustics is frequently used to quantify noise transmission paths and evaluate acoustic responses, the same transfer-path methodology can also be extended to investigate communication performance by characterizing both speech and noise propagation within an acoustic environment.

Using a simplified vehicle-cabin model, independent transfer paths were generated for a passenger-position speech source and an external engine-noise source. Responses extracted at virtual listener locations showed that speech and noise do not necessarily propagate through an enclosure in the same manner. The analysis revealed that relatively small changes in listener position can produce significant differences in received speech levels, noise levels, and ultimately the signal-to-noise ratio.

The investigation also demonstrated the importance of frequency-dependent acoustic behavior. As frequency increases and wavelength decreases, the acoustic field becomes increasingly spatially non-uniform. Reflection paths, local geometry, interference effects, and acoustic treatments all contribute to the response experienced by the listener. Consequently, communication performance may vary significantly even between listener locations separated by only a short distance.

An equally important outcome of the study is the recognition that Harmonic Acoustics generates far more than pressure-level predictions. The resulting transfer functions become reusable engineering assets that can be combined with a wide range of excitation signals, including:

• Recorded speech.
• Simulated speech.
• Engine-order content.
• Broadband noise.
• HVAC noise.

Rather than repeatedly solving the full acoustic model for every operating condition, engineers can leverage these transfer functions to rapidly evaluate alternative source scenarios and communication environments. In this sense, transfer functions become acoustic building blocks that support a broad spectrum of future investigations.

The workflow presented here also establishes the foundation for more advanced perceptual acoustic evaluations. Once source-to-listener transfer functions have been generated, they can be exported for additional analysis involving:

• Signal-to-Noise Ratio (SNR).
• Articulation-related metrics.
• Virtual listening studies.
• Sound-quality assessments.

By integrating Harmonic Acoustics with Ansys Sound, engineers can create virtual listening environments in which recorded speech, synthetic speech, engine noise, HVAC noise, and other acoustic signals are filtered through the simulated transfer paths. This capability provides a practical bridge between traditional acoustic simulation and human perception, enabling communication-performance evaluations before physical prototypes exist.

Potential applications include:

• Passenger communication studies.
• Aircraft crew communication assessments.
• Industrial control-room evaluations.
• Military vehicle communication studies.
• Construction equipment cabins.
• Heavy-equipment operator environments.

As organizations continue to embrace simulation-driven development strategies, the ability to evaluate not only how much noise is present but also how effectively occupants can communicate represents an important expansion of the role of acoustic simulation.

The ultimate engineering question is often not “How loud is the environment?” but rather “Can occupants communicate effectively within it?”

By leveraging source-to-listener transfer paths, Ansys Harmonic Acoustics provides a powerful framework for answering that question and extending acoustic simulation beyond traditional noise prediction into the realm of communication performance and speech intelligibility.

Need help evaluating acoustic performance with Ansys?

SimuTech Group’s acoustics experts can help your team use Ansys Harmonic Acoustics and Ansys Sound to evaluate noise transmission, speech propagation, transfer paths, and communication performance before physical prototypes are available.

Connect with SimuTech Group to discuss your acoustic simulation goals.